Improve clippy, and add more docs (#3306)

* Silence a few clippy warnings

* Use named threads

* Remove some deprecated functions

* Document Context and Ui fully

* Use `parking_lot::Mutex` in `eframe`

* Expand clippy.toml files

* build fix

crates/epaint/src/mutex.rs

@@ -374,6 +374,8 @@ where
 
 #[cfg(test)]
 mod tests {
+    #![allow(clippy::disallowed_methods)] // Ok for tests
+
     use crate::mutex::Mutex;
     use std::time::Duration;
 
@@ -414,6 +416,8 @@ mod tests {
 #[cfg(feature = "deadlock_detection")]
 #[cfg(test)]
 mod tests_rwlock {
+    #![allow(clippy::disallowed_methods)] // Ok for tests
+
     use crate::mutex::RwLock;
     use std::time::Duration;